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Depopulation kinetics of electron traps in thin oxynitride films
Abstracts
flowing oxygen with optimum condition : T l = 600°C for 5 min, T2 = 920°C for 8 min and 7"3 = 600°C for 5 min. The zero resistance temperatures of the superconducting thin films were achieved above 80 K. 120 keV O ÷ has been implanted into Y - B a - C u ~ ) as-deposited tilms. The electrical resistance of the films and their relations with both ion dose and temperatures were measured in situ. The initial values of resistance were strongly reduced with increasing O ÷ close. It can be interpreted that high resistance of as-deposited films may be partially attributed to the oxygen loss during sputtering. The resistance temperature curves of implanted films are characterized as a semiconductor with a negative temperature coefficient.
Luminescence studies in the process of preparing high Tc superconducting films with excimer laser ablation Fan Yongchang, An Chengwu, Lu Dongsheng and Li Zaiguang,
National Laboratory of Laser Technology, Huazhon9 University cf Seience and Technology, Wuhan 430074, Hubei, China The excimer laser ablation method for preparing high T~ superconducting films has a number of unique advantages. In order to understand the mechanism of laser ablation and the film growth, the luminescence spectra of the ejected particles from laser ablation of superconductor are studied in detail. In the experiment, when Y - B a - C u ~ superconductor target was bombarded with excimer laser beam, the target materials were ejected and a plasma plume was formed above the target surface. By measuring and identifying the luminescence spectra the types and the excited states of ejected particles in the plasma have been determined. Meanwhile, the velocity distribution and luminescence intensity distribution of the particles are also obtained by analyzing the time of flight spectra. The experimental results show that (i) the ejected particles are mainly in the form of big molecular clusters or solid fragments initially, and these clusters or fragments are finally dissociated into atoms, ions and small molecules by strong collision and interaction with the later portion of the laser pulse ; (ii) the flight velocity of particles is in the range of 105-106 m s l, much Easter than that from thermal evaporation; (iii) the maximum luminescence intensity position of the plume is far away from the target surface when the laser fluence increases. From these experimental results, the ablation mechanism and film growth principle are discussed.
Preparation and properties of carbon films and related multilayered films by laser beam deposition Ma Yurong, Guo Hua, Fang Kun and Fang Yihan, Department of
Physics, University of Science and Technology of China, Hefei 230026, China; and Xu Cunyi, Structure Research Laboratory, University of Science and Technology of China, Hefei 230026, China We present here novel results dealing with the application of a high power pulse laser in preparing thin films and related nmltilayer thin films.
The system consists of a Y A G pulse laser with a peak power of about 107 W, a vacuum target chamber and an optical emission spectrometer (OES) for measuring the optical emission of plasma during deposition. The target chamber contains focusing lenses, adjustable high voltage between the target, the substrate holder and the substrate heater. The targets can be precisely controlled in rotation. The deposition rate and uniformity of films have been examined by ellipsometry. Under properly chosen deposition parameters, the deposition rate is about 1.5 A s - ' and 1.0 A s - t for carbon and silicon films, respectively. The uniformity is good in an area of 10 mm in diameter. To produce uniform film is very important for laser beam deposition. Therefore, we have tried in several ways to improve the uniformity of the deposition system. The structure of carbon and silicon films is analyzed by Raman spectroscopy. It shows that the films are in a non-crystalline state characterized by a broad peak at 1560 c m - ' for carbon films and at 480 cm ~ for silicon films as the substrate temperature (T,) is less than 300°C. As Ts is above 300°C, a sharp peak at 1330 cm-~ for carbon films and at 520 cm ' for silicon films appears, indicating that crystallization occurs in the film. Thus, by properly controlling Ts and other parameters, diamond films can be prepared by laser beam deposition. Based on the studies of single layer films of carbon and silicon, multilayer structures of Si/C have been achieved. X-ray diffraction measurements prove their periodicity structure by the appearance of small angle Bragg diffraction. The modulation period derived from the Bragg formula agree well with that from the calculation of the deposition rate. The optical emission of plasma during deposition and the optical properties of our C/Si multilayer films have been also studied.
Depopulation kinetics of electron traps in thin oxynitride films H Wong and Y C Cheng, Department of Electronic Enyineering,
City Polytechnic of Hong Kon#, Tat Chee Avenue, Kowloon, Hon9 Kon9; and B L Yang and B Y Liu, Department of Physics, South China University of Technology, Guangzhou 510641, China This work reports both experimental and theoretical results of the depopulation kinetics of electron traps in silicon oxides annealed in ammonia ambient at a temperature of 1050°C for 30, 60, or 180 min. Results show that there is no significant difference for the nature depopulation process for different samples. However, for field-assisted depopulation, the optical and thermal emission coefficient and then the conductivity of the insulating films depend strongly on the process parameters. Specifically, a sample with longer annealing duration has a larger depopulation rate and is more sensitive to the electric field than the sample with the shorter period of annealing. These results indicate that the electron traps inside the oxynitrides can be filled and depopulated easily when an electric field is applied. The unstable nature of the oxynitride suggests that the present nitridation technique is not suitable for high quality insulator preparation although several enhancements of the electrical characteristics are found. The depopulation theory of the electron traps in thin oxynitride is also developed. By considering the re-trapping effect, most of the experimental observations can be explained with the present model. 1077
flowing oxygen with optimum condition : T l = 600°C for 5 min, T2 = 920°C for 8 min and 7"3 = 600°C for 5 min. The zero resistance temperatures of the superconducting thin films were achieved above 80 K. 120 keV O ÷ has been implanted into Y - B a - C u ~ ) as-deposited tilms. The electrical resistance of the films and their relations with both ion dose and temperatures were measured in situ. The initial values of resistance were strongly reduced with increasing O ÷ close. It can be interpreted that high resistance of as-deposited films may be partially attributed to the oxygen loss during sputtering. The resistance temperature curves of implanted films are characterized as a semiconductor with a negative temperature coefficient.
Luminescence studies in the process of preparing high Tc superconducting films with excimer laser ablation Fan Yongchang, An Chengwu, Lu Dongsheng and Li Zaiguang,
National Laboratory of Laser Technology, Huazhon9 University cf Seience and Technology, Wuhan 430074, Hubei, China The excimer laser ablation method for preparing high T~ superconducting films has a number of unique advantages. In order to understand the mechanism of laser ablation and the film growth, the luminescence spectra of the ejected particles from laser ablation of superconductor are studied in detail. In the experiment, when Y - B a - C u ~ superconductor target was bombarded with excimer laser beam, the target materials were ejected and a plasma plume was formed above the target surface. By measuring and identifying the luminescence spectra the types and the excited states of ejected particles in the plasma have been determined. Meanwhile, the velocity distribution and luminescence intensity distribution of the particles are also obtained by analyzing the time of flight spectra. The experimental results show that (i) the ejected particles are mainly in the form of big molecular clusters or solid fragments initially, and these clusters or fragments are finally dissociated into atoms, ions and small molecules by strong collision and interaction with the later portion of the laser pulse ; (ii) the flight velocity of particles is in the range of 105-106 m s l, much Easter than that from thermal evaporation; (iii) the maximum luminescence intensity position of the plume is far away from the target surface when the laser fluence increases. From these experimental results, the ablation mechanism and film growth principle are discussed.
Preparation and properties of carbon films and related multilayered films by laser beam deposition Ma Yurong, Guo Hua, Fang Kun and Fang Yihan, Department of
Physics, University of Science and Technology of China, Hefei 230026, China; and Xu Cunyi, Structure Research Laboratory, University of Science and Technology of China, Hefei 230026, China We present here novel results dealing with the application of a high power pulse laser in preparing thin films and related nmltilayer thin films.
The system consists of a Y A G pulse laser with a peak power of about 107 W, a vacuum target chamber and an optical emission spectrometer (OES) for measuring the optical emission of plasma during deposition. The target chamber contains focusing lenses, adjustable high voltage between the target, the substrate holder and the substrate heater. The targets can be precisely controlled in rotation. The deposition rate and uniformity of films have been examined by ellipsometry. Under properly chosen deposition parameters, the deposition rate is about 1.5 A s - ' and 1.0 A s - t for carbon and silicon films, respectively. The uniformity is good in an area of 10 mm in diameter. To produce uniform film is very important for laser beam deposition. Therefore, we have tried in several ways to improve the uniformity of the deposition system. The structure of carbon and silicon films is analyzed by Raman spectroscopy. It shows that the films are in a non-crystalline state characterized by a broad peak at 1560 c m - ' for carbon films and at 480 cm ~ for silicon films as the substrate temperature (T,) is less than 300°C. As Ts is above 300°C, a sharp peak at 1330 cm-~ for carbon films and at 520 cm ' for silicon films appears, indicating that crystallization occurs in the film. Thus, by properly controlling Ts and other parameters, diamond films can be prepared by laser beam deposition. Based on the studies of single layer films of carbon and silicon, multilayer structures of Si/C have been achieved. X-ray diffraction measurements prove their periodicity structure by the appearance of small angle Bragg diffraction. The modulation period derived from the Bragg formula agree well with that from the calculation of the deposition rate. The optical emission of plasma during deposition and the optical properties of our C/Si multilayer films have been also studied.
Depopulation kinetics of electron traps in thin oxynitride films H Wong and Y C Cheng, Department of Electronic Enyineering,
City Polytechnic of Hong Kon#, Tat Chee Avenue, Kowloon, Hon9 Kon9; and B L Yang and B Y Liu, Department of Physics, South China University of Technology, Guangzhou 510641, China This work reports both experimental and theoretical results of the depopulation kinetics of electron traps in silicon oxides annealed in ammonia ambient at a temperature of 1050°C for 30, 60, or 180 min. Results show that there is no significant difference for the nature depopulation process for different samples. However, for field-assisted depopulation, the optical and thermal emission coefficient and then the conductivity of the insulating films depend strongly on the process parameters. Specifically, a sample with longer annealing duration has a larger depopulation rate and is more sensitive to the electric field than the sample with the shorter period of annealing. These results indicate that the electron traps inside the oxynitrides can be filled and depopulated easily when an electric field is applied. The unstable nature of the oxynitride suggests that the present nitridation technique is not suitable for high quality insulator preparation although several enhancements of the electrical characteristics are found. The depopulation theory of the electron traps in thin oxynitride is also developed. By considering the re-trapping effect, most of the experimental observations can be explained with the present model. 1077